], Nannoplankton Res. 27 (2), 2005, pp.l49-157 © 2005 International Nannoplankton Association

149

JSSN 1210-8049 Printed by Cambridge University Press, UK

Rapid dissolution of calcareous nannofossils: a case study
from freshly cored sediments of the south-eastern Atlantic
Coastal Plain
Jean M. Self-Trail*, Ellen L. Seefelt
US Geological Survey, 926A National Center, Reslon, VA 20192, USA; *jstrail@usgs.gov
Manuscript received 1st July, 2005; revised rnanuscript accepted 11th August, 2005

Abstract Rapid dissolution of calcareous nannofossil assemblages from freshly cored sediments is documented
over a seven-month period. Examination of a series of smear-slides, made from raw material (a) on the day of coring, (b) 12 days after ·coring, (c) 42 days after coring, and (d) 222 days after coring, showed that dissolution had
already begun to occur 12 days after coring. Complete dissolution of calcareous nannofossil assemblages occurred
within seven months, in some cases. Dissolution of these assemblages resulted from the oxidation ol'iron sulphide,
driven by the presence of oxygen, and by the production of gypsum, which occurred during natural drying in storage. Oven-drying of samples greatly increased the rate of dissolution in some samples. The presence of organic matter, such as lignite, and pyrite in sample material also significantly accelerated the rate of dissolution. Loss of calcareous nannofossils through time is obvious when comparing slides originally containing frequent or common
assemblages. Abundant nannofloras underwent severe loss as well, although this is not as readily apparent in individual fields of view. By adjusting field-sampling methods, slide-making schedules and laboratory storage techniques, loss of calcareo~s nannofossils was minimised.
Keywords Calcareous nannofossils, dissolution, Atlantic Coastal Plain

1. Introduction
Over the past several decades, dissolution of in situ calcareous microfossil assemblages has been documented,
using a variety of both laboratory and field experiments.
Selective dissolution of calcareous nannofossils relative
to the lysocline was clearly documented by Berger(1973), who demonstrated the common occurrence of
coccolith dissolution on the sea-floor. Roth & Berger(1975) showed that etching, fragmentation and differential dissolution of calcareous nannofossils occurred in surface sediments from the Pacific Ocean at depths greaterthan 3km. Balsam (1982) and Stunt et al. (2002) recognised that fragmentation of planktonic foraminifera shells
increases with increased dissolution and that this carbonate fragmentation index can be used as a proxy for understanding deep-ocean circulation. Thierstein (1980)
explored the effects of dissolution on Late Cretaceous andDanian calcareous nannofossil assemblages, by exposing
samples at varying depths to corrosive deep-waters of thecentral North Atlantic. This study resulted in a dissolution
index of fossil calcareous nannofossils that is still applicable today.
Although loss of calcareous material at the sediment/water interface due to corrosive deep-water is one ofthe primary causes of calcareous nannofossil dissolution,other chemical processes have been shown to affectassemblage proportions, especially in the nearshore environment. Reaves (1986) documented that oxidation of ferrous sulphide minerals in intertidill mud-flats resulted in alowering of in situ pH values and consequently to undersaturation with respect to calcium carbonate. Lowered pH
values led to extensive dissolution of the shells of living

Mercenaria populations in the study area. Ku et al. (1999)
showed that sulphur cycling in organic-rich shelf carbonates is directly linked to carbonate dissolution. Organic
matter oxidation can result in a buildup of C02o which inturn can result in carbonate mineral undersaturation anddissolution (Canfield & Raiswell, 1991). A study by
Schulte & Bm·d (2003), on core material located well
above the lysocline, showed a direct link between variations in organic matter flux and calcite dissolution rate.
Additionally, the way in which cores and outcrop
material are stored following recovery, and the manner inwhich they are processed following sampling, can greatly
influence calcareous microfossil assemblages. Jutson(1995) noted that dissolution of nannofossils can occur indry, raw samples stored in laboratories and Geyh et al.
(1974) showed that storage of core material in cool ormoist conditions can promote bacterial activity and moldgrowth, which can lead to bacterial sulphate reduction.
Desiccation of core material can promote pro~uction ofincreasingly acidic interstitial waters, which in turn leads
to the precipitation of gypsum. Schnitker et al. (1980)
documented the rapid dissolution of benthic foraminifer
faunas in conjunction with the production of 'authigenic'
gypsum from cores in the Gulf of Maine. Andruleit et al.
(2000) focused on the dissolution of calcareous nannofossil assemblages related to post-sampling processing methods. They observed that a variety of factors, including carbonate content and primary preservation, contribute to thelong-term preservational state of calcareous nannofossil
assemblages.
The purpose of this study was to document the rate ofpost-coring dissolution that occurred in calcareous nanno-Self'Irail, Scefcll

150

fossil assemblages of freshly cored marine scdiments that
had been stored, and resampled, over a period of sevenmonths. The majority of micropalaeontologist' are probably unaware of the rapidity with which such chm1ges cantake place, and few have noted if long-term storage has
any effect on calcareous microfossil assemblages that areroutinely used for biostratigraphy, palaeoecology, or surface-water reconstruction. The results of this study
emphasise the need for greater awareness of potential
deleterious effects when selecting, preparing and storingmaterial for biostratigraphic and/or quantitative analyses.

2. Experimental procedures andmaterials
Two cores were examined for this study: E1izabethtown(BL-244) and Hope Plantation (BE-110), located in
Bladen and Bertic Counties, North Carolina, respectively(Figure 1). Thumbnail-sized sediment samples wereextracted from the central portion of core segments inorder to avoid the possibility of contamination from thebentonite-based drilling mud (pH?). Slides made fromcoastal plain sediments typically utilise standard settlingprocedures as outlined in Edwards et al. (1999).
However, smear-slides were prepared at a standard thickness for this study, in order to minimise any potential bias
in the sample set that might occur during processing.

remained in the sample bag, unprocessed, for a total of
222 days. The slide sets were then examined for calcareous nannofossils.
All slides were examined using standard light microscope techniques on a Zciss Photomicroscope 3. Initially,each slide was scanned at 1250x magnification to determine relative calcareous nannofossil abundance: abundant = >I 0 specimens per field of view (FOV); common= 1-10 specimens per FOV; frequent= 1 specimen per 110 FOV; rare = 1 specimen per 11-50 FOV. Following
this general scan, each slide was re-examined for 150
FOV, and counts of all identifiable nannofossils wererecorded. Severely broken specimens (less than halfremaining) were not included in the tally. Samples andslides arc curated at the US Geological Survey calcareous
nannoFossillaboratory in Rcston, Virginia (USA).

3. Results

Nineteen samples from Hope Plantation and seven samples from Elizabethtown were examined and found tocontain calcareous nannofossil assemblages. Additional
samples were examined for calcareous nannofossil content, found to be barren, and were not included in tl1is
experiment.
Examination of the calcareous nannofossil data showsa clear correlation between decreasing nannofossil abundance and time elapsed after coring(Tables 1, 2; Figures 2, 3). In all oF the
Elizabethtown samples, and 11 of the
Hope Plantation smnples, the number ofcalcareous
nannofossil
specimens
decreased significantly from the 'a' slides,
which were made on-site the day that core
was extracted from the ground, to the 'b'
slides, made 12 days later. In six of the
Hope Plantation samples, the 'b' slides
had more specimens than the 'a' slides,
and this most likely represents differences
"""'
"'"'
in smear thickness that resulted from the
preparation technique. In all but one slide
examined (NJ1928), abundance of calFigure 1: Map showing locations of the Hope Plantation (BE-110) and Elizabethtown(BL-244) Coreholes, North Carolina
careous nannofossils per 150 FOV
decreased from the 'a' slides to the 'd'A slide-processing schedule for the 26 fossiliferous slides (Plate 1). Sample abundance in NJ1928 remained
samples was established and a set of four slides (a, b, c the same throughout the study. In some cases, theand d) was made from each sample. The 'a' slides were decrease in calcareous nannofossil abundance was submade at the drill-site the same day the sample was cored. stantial, and sediment that was catalogued as having
The remaining sample material was then bagged and sent abundant calcareous nannofossils at the drill-site was barto the calcareous nannofossil laboratory, where it was ren in seven months (e.g. sample NJ1934, Hopestored at a constant temperature (24"C/75'F) and low Plantation core; Table 1).
humidity. The 'b' slides were made in the laboratory 12
In the Hope Plantation core, sediment that containeddays after the 'a' slides were prepared, the 'c' slides were abundant calcareous nannofossils when extracted on themade one month after the 'b' slides (42 days after coring), day it was cored saw an average 55.7% reduction in abunand the 'd' slides were produced six months after the 'c' dance within seven months (Table 3). Similmly, sedimentslides (222 days after coring), all from the same, bagged that was recorded as having common calcareous nannosample material that was used to produce the 'a' slides at fossils on the day it was cored showed a 60.8% average
the drill-site. In all, some sediment for each sample decrease in abundance, and samples having frequent or
~

.I

:I
I'

.Rapid dissolution of t~alcareous nannofossils
Snmple#Depth (m)H.slideb slidecslldedslldeNJI929

29.4

2439

3512

2068

1965

NJI930

31.1

3409

3111

2348

2472

NJJ931

32.6

3076

3042

3289

2351

NJI932

35.6

3308

3048

2797

2306

NJ1933

37.2

1582

1428

996

229

NJ1934

38.7

1618

1624

1471

0

NJ1935

40.4

2556

1682

1512

887

NJ1936

41.8

2373

1702

1334

141

NJ1924

197.0

84

22

15

22

NJJ925

197.1

63

59

39

26

NJ1926

197.7

6

6

0

0

Hope Plnntation Core~

NJ 1928

199.2

1

1

1

1

NJ1941

200.J

5

6

0

0

NJI949

206.3

33

45

1

4

NJI950

209.2

16

0

0

0

NJ1951

212.J

12

93

20

7

NJI952

214.0

316

167

234

170

NJ1953

217.8

292

375

200

122

NJ 1954

218.7

1167

1146

818

255

151

30000

~

0

~

00

~'<5l
00

u

20 000
Ol<8
u 0

'<-<
0

~
~

s "' 10 000
~

~

en

0
b

"

d

Slide

Figm·e 2: Histogram showing total number of calcareous nannofossil
specimens tallied from 'a', 'b', 'c', and 'd' slides, Hope Plantation core.
Note decreasing calcareous nannofossil numbers from 'a' slides (madeon day of coring) to 'd' slides (made 222 days after coring)
Figure 3: Histogram showing total number of calcareous nannofossil
specimens tallied from 'a', 'b', 'c', and 'd' slides, Elizabethtown core.
Note decreasing calcareous nannofossil numbers from 'a' slides (madeon day of coring) to 'd' slides (made 222 days after coring)
Elizabethtown Core

Table 1: Number of calcareous nannofossils per 150 FOV per slide,
Hope Planlation core

400

300
Sample#Depth (m)a slidebslidec slidedslideNJ1959

13.4

42

40

11

10

N.T1961

17.2

2

0

0

0

NJ1968

160.5

54

16

7

7

NJ1969

162.4

87

56

40

8

NJ1972

165.0

142

138

64

24

NJ1970

166.0

10

9

8

4

NJl971

168.0

16

5

11

11

Table 2: Number of calcareous nannofossils per 150 FOV per slide,
Elizabethtown core

200
100

0
b

d

Slide
Sample#Depth (m)a slideb.slidec.slided slideNJ1929

29.4

47

52

71

90

Nll930

31.1

42

54

63

68

NJI931
NJ1932

32.6

62

35.6

so
47

75

68
RI

72
88

NJI933

37.2

78

94

113

143

NJI934

38.7

87

90

106

0

NJI935

40.4

64

76

85

121

NJI936
NJ1924

41.8

RS

106

135

164

. 197.0

141

230

321

354

NJ1925

197.1

170

206

260

276

NJI926

197.7

Sample#Depth (m)'7t! Reduction

NJ192919.4

NJ1930

29.4
31.[

27.5

NJ1931

32.6

23.6

NJ193235.6

30.3

NJJ933
NJ1934

37.2
38.7

85.5

N.T1935

40.4

100.0
65.3

NJ193641.8

94.0

NJI928199.2

NJI924

197.0

73.8

NJJ941

200.1

NJ1925

197.1
197.7

58.7

N.T1949

206.3

100.0

NJ1950209.2'

NJ1951

212.1

346

366

968

1431

NJI952

214.0

158

190

204

223

NJI953
NJ1954

217.8

157

218.7

82

160
112

175
139

165

NJI926
NJ1928199.2

NJI941

200.1

100.0

NJJ949

206.3

87.9

NJI950

209.2
212.1

100.0

NJI951
NJI952

Table 3: Percent reduction in Hope Plantation
calcareous nannofossil
assemblages belwcen 'a'and 'd' slides (approximately seven months).
*Indicates no change incalcareous nannofossil
abundance

Too S!>lll"Se for count~

193

41.7

214.0

4<>.2

NJ1953

217.3

53,2

NJ1954

218.7

78.1

Table 5: Number of calcareous nannofossil fragments per 100 whole
nannofossils per slide, Hope Plantation core

Table 4: Percent reduction in Elizabethtown calcareom; nannofossil
assemblages between 'a' and 'd' slides (approximalely seven months)
Sample#Depth (m)%Reduction

NJI95913.4

76.2

NJI961

17.2

100.0

NJI968160.5

NJI969

162.4

87.0
90.8
33.1

NJI972165.0

NJ1970

166.0

60.0

NJ1971

168.0

100.0

a slide I b slide I c slide I d slide

Sample#Depth (m)NJI95913.4

NJI961

17.2

NJI968160.5

305

NJI969162.4

195

NJ1970166.0

NJ1971

168.0

N.T1972

165.0

344

I

I

I

866
361
s49
Too S1>arse fo1· counts
575

I 235

I

1017
328

I

1220
983

Too sparse fm· counts

135

I

211

I

323

453

Table 6: Number of calcareous nannofossil fragments per lOO whole
nannofossils per slide, Elizabethlown core

152

Self· Trail, Secl'ell

Jericho Run :Formation

Donoho Creek Formation?
250

2SO

250

mo

200

200

200

150

150

!50

!50

" 100

10()

so

50

ro

»

0

NJ193~

0
40

80

60

60

80

NJ1932100~

50-b~-<f'"'-,~-',"_·~s,.~
40

100

100

~

250

NJ1931

~

50

diss.

0

diss.

~

)

0

lOO

40

80

60

100

6(1

40

80

100

150

200

Tarhcel Formation
250

250

NJ1933250

NJ1934250

NJ1935

NJ1936

200

200

~10

2()()

~ 150

150

150

150

0

lOO
50

100

100

~

~

so

diss.

0

so

lOO

150

200

50

so

diss.

I'

0

100

~

50

diss.

0

100

150

200

100

\50

so

200

100

Clubhouse Formation
250

250

NJ1924

~m

200

150

0100

Vl

~

~

dbs./

so

250

NJ1925

r

200

150

150

150

100

100

100

50

50

0

0

~

so

diss:_£

0
50

150

250

so

350

250

200

200

L'lO

150

;:::.,100

100

•2\

~

so
so

!50 250 350
Fragments per 100
whole specimens

350

'

150

50

250

350

whole spccunens

diss.

50

!50

'

,;o

250

Fragments per 100
whole specunens

250

NJ1968250

NJ1969

200

200

200

200

~ 150

150

150

150

100

100

lOO

~

50

diss.

0
300

~

50

500

700

900

whole spccunens

diss.

so

930

0
130

0

130

530

930

1330

Fragments per 100
whole specimens~

NJ1972

100

~

50

dios.

0

Fmgments !?er lOO

I~

Pleasnnt Creek Formation
250

Cl

I

NJ1952 ~Figure 4: Plots of nannofossil fragments per lOO whole calcareous nannofossil
specimens against number of days before slide preparation, Hope Plantation core.
Note that increasing calcareous nannofossil dissolution is to the dght (indicated byarrows). Samples from each fotmation were plotted al the same scale, except for
NJ195J (Clubhouse Formation), which had to be plotted at a different scale due tothe excessive number of fragments recorded. Sample NJ1934 has no data point for
the 'cl' slide (222 days) because it was barren. See Table 1 for depth of samples incore

Fragments per 100

NJ19591100 1500

Fragments per 100
whole specimens

diss.

Bladen Formation
250

300 700

~

_j
0

~

250

~ NJ1954

so-

diss.

0

ISO

250

~NJ1953250

NJ1951

200

130

530

1330

Fragments !?er 100
whole speC111lens

~

lf

dlss.

530

930

1330

Fragments per 100
whole specin1ens

Figure 5: Plots of nannofossil fmgments per lOO whole calcareous nannofossil specimens against number of days before slide preparation,
Elizabethtown core. Note that increasing calcareous nannofossil dissolution is to the right (inclicutec\ by arrows). See Table 2 for depth of samples incoreRapid dissolution of a~alcan.•4ms nunnofossils

rare calcareous nannofossil assemblages when freshly
cored record an average 70.3% reduction in abundance.
Of the 19 samples examined from Hope Plantation, four
were barren and eight had calcareous nannofossil assemblages reduced by more than 50% within 222 days after
coring (Table 3). The remaining seven samples experienced calcareous nannofossil assemblage reduction of
between 19.4 and 46.2%. Samples from the
Elizabethtown core contained only frequent or rareassemblages on the day of coring. Of the seven productive
samples, two were barren and the remaining five had calcareous nannofossil assemblages reduced by 60.0% ormore within 222 days after coring (Table 4). Calcareous
nannofossil assemblages from Elizabethtown werereduced by an average 85.3% within seven months.
As a means of estimating dissolution and removing
any bias from the specimen counts that may have been
introduced during the slide-making process, calcareous
nannofossil fragments per lOO whole nannofossil specimens were counted and plotted against number of days
after coring (Figures 4, 5; Tables 5, 6). Several clear patterns emerge from this dataset. In the Hope Plantationcore, samples that remained abundant throughout theentire 222 days experienced the most rapid dissolution
within the first 42 days following coring (Figure 4;
Samples NJ1929, NJ1930, NJ1931 and NJ1932), and thendissolution rates between 42 and 222 days slowed considerably. Abundant samples from different formations
showed slight variations in dissolution rates. For example,
Sample NJ1932, horn the Donoho Creek Formation,
experienced rapid dissolution in the first 12 days, which
was then followed by moderate to slow dissolution rates
over the next 112 days. However, Samples NJ1929,
NJI930 and N.ll931, from the Jericho Run Formation,
experienced rapid to moderate dissolution for the first 42
days, and moderate to s1ow rates of dissolution for theremaining six months. In comparison, dissolution rates
were higher in samples from marginal (Tar Heel
Formation: NJ1933, NJ1934, NJ1935 and NJ1936) andshallow marine settings (Clubhouse Formation: NJ1952,
N.ll953 and NJI954), as evidenced by the increased number of tl-agments per lOO whole specimens counted(Figure 4). Dissolution rates from the Clubhouse
Formation were high in the upper part of the formation(Figure 4; NJ1924, NJ 1925, NJ1951), as evidenced by the
rapid increase in fragmentation seen in Sample NJ 1951,
but remained slow in the basal part of the formation(NJ1952, NJ1953, NJ1954), despite the lack of any obvious lithological differences between the basal and upperparts of the sections (Weems et al., in press). This patternis also seen in samples from the Elizabethtown core,
which shows rapid dissolution rates at the top of the
Pleasant Creek Formation and slow to moderate rates near
the base of the section (Figure 5). Sample NJ1959 fromthe Bladen Formation (Elizabethtown core) has an assemblage that records very slow dissolution rates for the first
12 days, followed by rapid dissolution over the next six

153

months. As expected, the number of fragments per 100
whole specimens increased as calcareous nannofossil
abundance decreased. High fragment amounts in sediments with low initial abundances suggest that sedimentswith low initial calcareous nannofossil abundances most
likely experienced in situ, natural, dissolution before coring (e.g. NJ1951, NJ1924; Figure 4). Overall, the rate andamount of dissolution was higher in sediments from the
Elizabethtown core.
In almost every sample, dissolution rates were rapid in
the days and weeks following coring, and then decreased
slowly over time, usually after 42 days. Complete dissolution of calcareous nannofossils was rare. This pattern iswhat would be expected if conditions stayed constant during storage while the carbonate system equilibrated. If
equilibrium was attained quickly, then complete loss of
calcareous nannofossil assemblages was avoided. This
could explain why some sample material that has been instorage for over 50 years still has nominal calcareous nannofossil assemblages (JMS-T, unpublished data).

4. Discussion
Chemistry and lithology are the two most likely controlling factors in post-coring diagenesis of calcareous nannofossil assemblages in the studied suite. An understanding of the processes that occur during chemical interactions between oxygen, water, iron and calcite is necessary
in order to understand the sequence of events that can leadto calcareous nannofossil dissolution.

4.1 Chemistry
Dissolution of calcareous nannofossils in the studied
cores is most likely occurring due to a combination of
three separate processes: pyrite oxidation, gypsum production, and bacterial activity. Sediments of the southeastern Atlantic Coastal Plain were deposited in environments that ranged from ±1uvial to neritic, and which commonly contain tcrrcstrially-dcrived material in the form ofpollen and spores (Christopher & Prowell, 2002) and lignite. Total organic content in any cored interval can be as
high as 30% (Self-Trail et al., 2004; Weems et al., inpress). Sediments rich in organic matter commonly contain disseminated pyrite and/or pyrite and marcasite nodules. If the sediments contain pyrite or marcasite, when
the core comes in contact with oxygen, pyrite oxidation
can occur, as demonstrated by the chemical equations:
FeS2 + 3.50 2 ~ H 20 = Fe2+ + 2S042- + 2H+(1)

Fe2+ + 0.2502 + 2.5H20 = Fe(OH) 3 + 2I-J+(2)These reactions generate acidity, which dissolves calcium
carbonate, as demonstrated by the chemical equation:
CaC0 3 + J-I+ <=> Ca2+ + C0 2(g) +OH-

(3)

154

ScU'~ Trail, Seefdt

Dis...;;olution will occur as long as oxygen and iron areavailable to diive the reaction, or until all catcium carbonate is dissolved.
In addition to pyrite oxidation, precipitation of gypsum occurred where conditions were suitable, causing
further degradation of the sample material. Gypsum precipitated upon desiccation of interstitial water, which usually occurred during sample storage. In organic-rich sedimcnts under arid conditions, gypsum has been noted toform in a matter of hours (Briskin & Schreiber, 1978).
Precipitation is encouraged by both natural evaporationand forced drying in convection ovens. Free calcium(Ca2+) is supplied by the dissolution of calcareous fossils(molluscs, calcareous nannofossils and foraminifera), andsulphate (S0 42+) is produced from pyrite oxidation, following the equation:(4)

process to varying degrees. Examination of calcareous
nannofossil samples, with regards to lithology and sedimentology, shows that several accessory components play
an important role in calcareous nannofossH dissolution.
Samples free of lignite or pyrite typically contain moreabundant and diverse calcareous nannofossil assemblages. This is not surprising, since the oxidation process
is significantly decreased in the absence of organic material and pyiite. Presence of pyrite and/or lignite is moresignificant than grain size, as is clearly demonstrated bysamples examined from the Jericho Run and Tar Heel
Formations in the Hope Plantation core (Figure 4; Table7) and the Bladen and Pleasant Creek Formations in the
Elizabethtown core (Figure 5; Table 8). The fine-silly,organic-poor sands of the Jericho Run Formation preserved calcareous nannofossil assemblages better than theclayey silts of the slightly organic Tar Heel Formation(Table 7) and the organic-rich, clayey silts and silty clays

Since desiccation of samples may% Slicll matel'ial% 01·gnnics% l'hosphaie
Liillology% Glauconitc% l'yrite
Depih(m)Srun Jlcfl
sand, f c
0
0
10
<I
0
NJl929294
promote supersaturation with respectsand, f-m
5
0
0
<I
0
Nll93031.1
to gypsum, drying of samples could
500sand, f-m
0
NJ1931
32.6
sand, f30
0<I<I
NJ\93235.6
result in a greater loss of calcareous"2
clayey silt
0
2
0
<I
37.2
NJl933nannofossil data.
0
clayey silt
20
2
NJI9343H.7
clayey sill
0
2
0
I
2
A third means of sample degradaNJ1935
40.4
clayey silt
2
0
I
2
0
4l.H
NJ\936tion is through bacterial activity,
micrite
0
0
0
10
2
197.0
NJI924
which can occur OOth in situ andmicrite000102N.ll92S
197.1
sand, vf
00
0
20
NJ\926
197.7
immediately following coring.
sand, vf
0
0
0
5
0
199.2
NH928
Bacteria can tolerate a wide range of
3
sand, vf
0
0
7
<I
NJ1941200.1
smut, vf
00
0
2
<I
NJ1949206.3
pH conditions, most notably sulsand, vf-f
0
0
0
10
2
NJ\950209.2
phide-oxidising bacteria, which can000sand, vf-i'
10
2
212.1
NJI951
sand, vf-f
<I
0
0
3
0
survive in an acidic pH range of 3.0
NJ19.'i2
214.0
sand, vf-f
0
0
>10
0
<I
NJ1953217.8
to 4.0 (Chapelle, 1993). Additionally,
sand, vf-f
0
>10
0
0
<I
218.7
NJI9S4'iron bacteria', a group of aerobic
bacteria that oxidises ferrous iron as
Table 7: Lithology and sedimentology of samples from the Hopea source of energy and that live at the interface of anaerPlantation core. Percentages are estimates obtained from examination of core material on-site (Weems et al., in press)
obic and aerobic environments, become actiVe when aconstant source of oxygen is supplied. These microorganTable 8: Lithology and sedimentology of samples from theisms can be activated directly following drilling, when
Elizabethtown core. Percentages are estimates obtained from examsubsurface sediments are exposed to oxygen. If dissolved
ination of core material on-site (Self-Trail et al., 2004)
Fe2+ is present, as is often the case in
Lithology% Ghnu:onitc %Pyrite % I'hos bale % SI1cll lll!ltcrlal% OrgaJJics
inner to middle neritic and/or marSam!Jlef/ Dcptll(nl02NJ1959134"ilt,ca\cm.,DLls000
ginal marine sediments, then oxida00
NJI96117.2
snnd,f-m
0
0
0
160,5
7
NJ\968clayey slit
9tion can occur, as demonstrated by
20"3
5NJ\969162.4
siltyclay020
Equation 2, above. Although dissolu3
4
NJ\972\65.0
siltyday
0
2
0
<I
\66.0
NH970
silly day20
I0tion of calcareous nannofossils has
168.0
sill c!!_t)'_
NJ\971<I
30
00
not yet been directly linked to bacterial activity, it is clear from theexperiments and observations of Chappelle (1993) that of the Bladen and Pleasant Creek Formations, which wereiron-oxidising bacteria exist in abundance in freshly cored highly destmctive to calcareous nannofossil assemblages
sediments of the south-eastern Atlantic Coastal Plain, and (Table 4).
it is possible that these microorganisms are contributing to
The presence or absence of glauconite, phosphate
the oxidation process that ultimately results in dissolution and/or shell material, all common constituents in sediof calcareous nannofossils.
ments representative of inner to outer neritic environ-""

4. 2 Lithology
Sediment type can affect the post-coring dissolution

ments of deposition, does not appear to be significant withregard to calcareous nannofossil dissolution.Varying
amounts of these constituents occur in samples with low

I
I

I

Rapid dissolution of cakareous nannofossiis
incidence of calcareous nannofossil dissolution, as well as
high incidence of dissolution in our suite.

5. Conclusions
Analysis of calcareous nannofossil assemblages from
freshly cored sediments from the south-eastern Atlantic
Coastal Plain over a period of seven months clearly documents their rapid dissolution. In some cases, dissolution
is so rapid that biostratigraphic analyses have been compromised and samples known to contain calcareous nannofossils from temporary smear-slides made in the field
are barren by the time permanent slides are made in thelaboratory. The results of this study imply that samples
extracted from core material that has been in storage forgreater than six months could possibly contain calcareous
nannofossil assemblages that have been severely compromised, especially if organic matter is present. Thus,
research that relies on biostratigraphic or statistical analyses of calcareous nannofossil assemblage data fromorganic-rich sediments should be conducted on freshly
cored samples, in order to preclude diagenetic affects
from potential geochemical reactions.
Samples containing abundant calcareous nannofossils
are typically assumed to be relatively free of diagenetic
alteration. However, examination of Samples NJ1929NJ1932 (Table I) clearly shows that this is not entirely
true. The nannofloras remained abundant throughout the
time-frame of the experiment, yet are clearly undergoing
dissolution, as evidenced by the decreased number of
specimens per 150 FOV and by the increase in fragmcnt:wholc specimen ratio through time.
The observation that rapid dissolution of calcareous
nannofossil assemblages from the Hope Plantation andElizabethtown cores occurred within the first two weeks
following coring is of importance to micropalaeontologists. However, by adjusting our field sampling and sample storage methods, loss of data was minimised (JMS-T,
unpublished data). Recognition of factors that can contribute to the rapid dissolution of calcareous nannofossils(e.g. the presence of pyrite in sedimcnts) can be used todictate changes in sample storage and/or processing methods. Guidelines include: (I) prone sediment samples
should be processed as quickly as possible following coring. High quality smear-slides can be produced in thefield with minimal effort; (2) exposure of prone sample
material to oxygen should be limited. Oxygen provides
the energy needed to drive deleterious chemical and bacterial reactions. Freeze-drying or vacuum-packing samples may provide a temporary means of transporting samples from the field to the lab without the loss of additional assemblage data; (3) if smnples are very wet and need
to be dried before storage, use low heat ( <50"C) andremove samples quickly once dry. Gypsum formation
occurs naturally during air-drying, but can also be accelerated with the addition of heat; (4) recognise that coresamples that have remained unprocessed for any length oftime may already be compromised, even if the nannoflo-l155

ras are abundant and look pristine (e.g. Samples NJI929NJ1932). There is uo way of knowing how much dissolution has occurred without first viewing a comparison
smear-slide made on the day of coring.
This study represents only the first step towards
understanding the effect that post-sampling dissolution
has on calcareous nannofossil assemblages. Comparative
studies, focusing on differing lithologies and environmental settings are needed, and both outcrop and cored sediments should be examined. Additionally, the effects ofpost-sampling dissolution on species diversity and assemblage composition need to be documented from a varietyof environmental settings. Self-Trail and Seefelt (in prep.)are currently investigating changes in assemblage dynamics from the Hope Plantation and Elizabethtown samples.

Acknowledgements
The authors wish to thank Gloria Ferrell (USGS) and Heather
Hanna (NCGS) for insights into the chemical reactions that takeplice between sedimentary organic matter, calcium carbonate
and gypsum. We are grateful to Eugene F. Cobbs Ill (USGS) for
taking the time to re-core marine sediments from the
Elizabethtown core. In-depth discussion between attendees of
the Dissolution of Calcareous Nannofossils: Causes andSolutions Workshop (INA 10) was invaluable. An em·ly draft ofthis manuscript was reviewed by Laurel M. Bybell (USGS) and
G. Lynn Brewster-Wingard (USGS). This paper benefited fromthe thoughtful reviews of Dr. David Jutson (RWE-Dea) and an
anonymous reviewer.

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Rapid dissolution of cakareous nannoi'ossils

157

Plate 1
Representative FOV pictures of an abundant (NJ1936), common (NJ1954) and frequent (NJ1969) sample: (a) on day of coring;(b) 12 days after coring; (c) 42 days after coring; and (d) 222 days after coring. Note successive decrease in calcareous nannofos~
sil abundance from 'a' to 'd' slides in all three examples. Light microscope pictures were taken at 1250x magnification and do not
represent an entire field of view